Detection of microcracking in concrete by acoustic emission

An acoustic emission (AE) is a very localized, rapid release of strain energy in a stressed material. This energy release causes stress waves to propagate through the specimen. These stress waves can be detected at the specimen surface and analyzed to deduce the magnitude and the nature of damage present in a material. Acoustic emissions result from microcracking, dislocation movement, phase transformations, and other irreversible changes in a material. As a nondestructive testing method AE measurements have been used to assess the structural integrity of existing structures. In this paper, however, the focus will be on its use as a laboratory tool to characterize material damage. This paper will present a brief introduction to acoustic emission measurement techniques and its use in a Northwestern University investigation of damage in concrete.